Seiko 7A38 - by the numbers

Subtitle

Forums

Post Reply
Forum Home > Parts Info, Tech Tips and Tinkering > You need hands .... and sometimes need to pull them off.

Seiko7A38
Site Owner
Posts: 14137

Someone asked me on the phone tonight about pulling and replacing hands (which until you've actually tried it seems pretty daunting).

This is a good online tutorial from the PMWF watch school. I read this well, before I ever bought my own tools and tried it out for myself:


http://www.pmwf.com/Watches/WatchSchool/ HOW TO remove and replace hands and dial.htm


February 10, 2012 at 5:33 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14137

I personally use* a 'Presto' hand(s) lifter to pull the main handset (all three - hour, minute and sweep second) all off together.

I bought a pair of Horotec 1.0mm wide chronograph hand levers - their part number MSA 05.009 - not cheap but lovely tools to use. 

For re-fitting hands, you can of course use pegwood, or the point of a plastic tipped Biro, and all kinds of other implements.

Again, I splashed out and purchased a set of three A*F hand setting tools. Their part number 174.316 (Cousins p/n H31401).

See: http://www.cousinsuk.com/catalog/6/0/1291/2327.aspx#select


*I also bought one of the Indian-made 'pantograph' style hand lifters off eBay, but rarely use it, and don't get on with it. :(

February 10, 2012 at 5:44 PM Flag Quote & Reply

7ARCool ©
Member
Posts: 168

On the topic of hands, I require a few main chrono second hands, are these available and are many interchangeable from other Seiko models as they do look similar?

February 19, 2012 at 5:53 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14137

Some are, Chris, but not many. Search Cousins on Seiko 13SC0*** and you'll find a couple of similar ones.

I know for a fact that 7T32 sweep second hands will fit a 7A38 - they're the same (nominal) 0.20mm bore. ;)

February 19, 2012 at 7:40 AM Flag Quote & Reply

Rob Benham
Member
Posts: 281

I read right through and picked up on not using a hole too big as it might bend the second hand, and blowing the lume off!!  But what I still don't know is just how much pressure I can apply to the sweep seconds shaft.  I managed to lift it off okay and have examined the shaft and wheel, but I don't really know if there is a positive click as it is pressed down.  I just do not want to ruin the jewel/bearing having got this far.

.

Registering the hand.  I had come to the conclusion that if it was moved while correctly pressed on, it took up that new position as far as the chip was concerned.  You'll gather I'm very hazy about this, but having gone through the zeroing procedure, I noticed the hand was about half a second too advanced.  I moved it back and it settled on a minus position and this became the new datum.  At no time did it fall on the exact mark.

.

I assume it's like an ordinary watch and must be pressed on exactly on the mark.  Can someone confirm, and give a clue as to the pressure that may be applied, por favor.

February 9, 2014 at 1:47 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 14137

Rob. If you've had a dial / movement out of the watch case and tried gently nudging the hands between marks using something non marking, like a wooden cocktail stick, you'll feel a certain 'lumpiness'. I believe that lumpiness is caused by the residual magnetism in the respective rotor / stator of that particular gear train, rather than backlash in the gear teeth - and that it is that magnetic attraction which determines the resting position of the hand, relative to the dial marks. It's most noticeable with the 30 minute and 1/10 second sub-dials and less so with the constant seconds sub-dial (with the crown pulled out to whichever setting position - which right now, I can't remember off the top of my head). It's also just  perceptible with the chrono' sweep second hand, but because of the length of that hand (hence much less leverage required) harder to detect. It's not connected with the CMOS IC as I think you were inferring.


When re-fitting hands, I drop them gently in place, press them down just enough for the hand collet to bite on the shaft and use that lumpiness to help align the hands with the marks, by giving the hand a couple of nudges around the sub-dial / dial. Once I'm satisfied with the alignment (it may take a couple of goes), I press the hand home properly. The amount of additional pressure is impossible to quantify, but it is minimal. Too much pressure results in bent hands and at worst damaged or dislocated jewels.

Been there, seen it done (by somebody else). Try reading that old RLT thread from post #14 onwards.


February 9, 2014 at 6:10 AM Flag Quote & Reply

You must login to post.